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Sexual Reproduction of the Flowering Plant

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1 Sexual Reproduction of the Flowering Plant

2 Learning objectives(1/4)
State the structure & function of the floral parts including: Sepal, petal,stamen,carpel) State that the Pollen grain produces male gamete. State that the Embryo sac produces an egg cell & polar nuclei. Define the terms: pollination, self-pollination Outline methods of pollination including: cross-pollination & self pollination

3 Learning objectives(2/4)
Define the term: fertilisation. Outline seed structure & function of following: testa, plumule, radicle, embryo, cotyledon Explain embryo & food supply (endosperm or seed leaves) Classify plants as monocotyledon or dicotyledon & distinguish between them. Make reference to non-endospermic seed. Outline fruit formation. Outline seedless fruit production

4 Learning objectives(3/4)
Outline fruit & seed dispersal and give with examples of wind/water/animal/self dispersal Explain & emphasise the need for dispersal Define the term dormancy. State advantages of dormancy. Explain dormancy in agricultural & horticultural practice. Define the term: Germination. Explain the factors necessary for and role of digestion and respiration in germination. Outline the stages of seed development

5 Learning objectives(4/4)
State that vegetative propagation is asexual reproduction Give 1 example of vegetative propagation from stem, root, leaf, bud Compare reproduction by seed and by vegetative reproduction Outline 4 methods of artificial propagation in flowering plants

6 Reproduction in Flowering Plants
Two Types of Reproduction: Asexual Reproduction Sexual Reproduction

7 Asexual Reproduction Asexual Reproduction involve only one parent The offspring are genetically identical to the parent i.e. a clone Strawberry plants

8 Sexual Reproduction Sexual Reproduction involves the union of two sex cells called gametes. Gametes are haploid cells capable of fusion A zygote is formed when two haploid gametes fuse (join) together. The offspring of sexual reproduction are not genetically identical to the parents

9 Structure of the flower

10 Structure of the flower

11 Structure of the flower
Petal Anther Filament Stamen Stigma Style Ovary Ovule Sepal Carpel


13 Function of floral parts
Sepal : To protect the flower (and to prevent it from drying out Petals : To attract insects to the flower for pollination

14 Function of floral parts
Stamen : To produce the pollen grains in the anthers. (Each pollen grain produces two male gametes, one of which can fertilise an egg cell)

15 Function of floral parts -Stamen
Anther Produces pollen Filament Holds the anther in place

16 Function of floral parts
Carpel : To produce the ovules (Each ovule contains an egg cell inside an embryo sac)

17 Function of floral parts - Carpel
Stigma Where pollen lands after pollination Style Pollen travels down this Ovary Contains ovules

18 Function of each part of flower
Receptacle Sepals Petals Nectaries Stamens Carpels

19 Pollination

20 Pollination Transfer of pollen from the anther to the stigma of a flower of the same species

21 Pollination Self pollination
Transfer of pollen from an anther to a stigma of the same plant Cross pollination Transfer of pollen from the anther to the stigma of a different plant of the same species

22 Methods of pollination
Animal Pollination Wind Pollination

23 Adaptations for animal (insect) pollination
Petals brightly coloured, scented with nectaries Small amounts of sticky pollen Anthers inside petals Stigmas sticky, inside petals


25 Adaptations for wind pollination
Petals small, not coloured brightly Anthers outside petals Stigmas large, feathery and outside petals Pollen Large numbers, light, dry and small

26 Adaptations for wind pollination

27 Fertilisation

28 Fertilisation Fertilisation is the fusion of the male (n) and female (n) gametes to produce a zygote (2n) The pollen grain produces the male gametes Embryo sac produces an egg cell and polar nuclei

29 The pollen grain produces the male gametes
Embryo sac produces polar nuclei and an egg cell Embryo sac Polar nuclei Egg cell

30 Stigma Style Ovary

31 Embryo Sac Polar nuclei Egg Cell

32 Pollen Grain

33 Pollen Tube

34 Generative Nucleus Tube Nucleus


36 Mitotic division of generative nucleus to form 2 male gametes
Tube nucleus disintegrates


38 1 Male gamete fuses with the 2 polar nuclei to form the triploid endosperm nucleus
1 male gamete fuses with the egg nucleus to form the diploid zygote

39 3N endosperm nucleus Double fertilisation 2N Zygote

40 Endospermic & Non-Endospermic Monocots & Dicots
Seed formation Endospermic & Non-Endospermic Monocots & Dicots

41 Seed Formation The zygote grows repeatedly by mitosis to form an embryo An embryo consists of a plumule (future shoot), a radical (future root) and cotyledons (food stores needed for germination) 3N endosperm nucleus 2N Zygote

42 Seed Formation The endosperm nucleus (3N) divides repeatedly to form the endosperm in endospermic seeds. This endosperm acts as a food store for the developing seed e.g. maize 3N endosperm nucleus 2N Zygote

43 Seed Formation In non-endospermic seeds the endosperm is used up in the early stages of seed development so the food is stored in the cotyledons e.g. bean 3N endosperm nucleus 2N Zygote

44 Seed Formation Endosperm Food store for developing embryo
Embryo Plumule, radicle, cotyledons Integuments, becomes the seed coat

45 Seed Formation If all the endosperm is absorbed by the developing embryo the seed is a non endospermic seed e.g. broad bean

46 Seed Formation If all the endosperm is not absorbed by the developing embryo the seed is an endospermic seed e.g. Maize

47 Seed types and structure
embryo Plumule (immature shoot) Radicle (immature root) Cotyledon (food supply or seed leaf) endosperm Food store All seeds In some seeds

48 Endospermic Seed e.g. Maize
Seed coat (testa) Cotyledon Endosperm Plumule – will develop into a new shoot Radicle – will develop into a new root

49 Non-Endospermic seed e.g. Broad Bean
Seed coat (testa) Cotyledon Plumule Radicle

50 Non–endospermic and Endospermic seed
Cotyledon Plumule Radicle e.g. Broad Bean e.g. Maize

51 Classification of seeds
Classified according to two features: Number of cotyledons (Seed leaves) Monocotyledon – one cotyledon E.g. Maize Dicotyledon - Two cotyledons E.g. Broad bean Presence of endosperm Present – Endospermic e.g. maize Absent – Non-endospermic e.g. broad bean

52 Broad Bean – Non-Endospermic Dicot
Testa 2 Cotyledons

53 Differences between monocots and dicots
Feature Monocot Dicot Number of cotyledons 1 2 Venation Parallel Reticulate (Net) Vascular Bundle arrangement Scattered In a ring Number of petals Usually in multiples of 3 Usually in multiples of 4 or 5



56 Fruit formation Seedless fruits Fruit and seed dispersal

57 Fruit Formation The ovule becomes the seed The ovary becomes the fruit

58 Fruit Formation A fruit is a mature ovary that may contain seeds
The process of fruit formation is stimulated by growth regulators produced by the seeds

59 Seedless Fruits Genetically
Can be formed in two ways Genetically Either naturally or by special breeding programmes e.g. seedless oranges

60 Seedless Fruits Growth regulators e.g. auxins
If large amounts of growth regulators are sprayed on flowers fruits may form without fertilisation e.g. seedless grapes

61 Fruit and seed dispersal
Need for dispersal Minimises competition for light, water etc. Avoids overcrowding Colonises new areas Increases chances of survival

62 Types of dispersal Wind Water Animal Self

63 Methods of dispersal Wind Sycamore and ash produce fruit with wings
Dandelions and thistles produce fruit with parachute devices Both help the disperse the seeds more widely using wind

64 Methods of dispersal Water
Light, air filled fruits that float away on water E.g. coconuts, water lilies

65 Methods of dispersal Animal Edible fruit
Animals attracted to bright colours, smells and food Seed passes through digestive system unharmed E.g. strawberries, blackberries, nuts

66 Methods of dispersal Animal Sticky fruit
Fruits with hooks that can cling to the hair of an animal and be carried away E.g. burdock, goose grass

67 Methods of dispersal Self
Some fruits explode open when they dry out and flick the seed away E.g. peas and beans

68 Dormancy and germination

69 Dormancy (definition)
A resting period when seeds undergo no growth and have reduced cell activity or metabolism

70 Dormancy (advantages)
Plant avoids harsh winter conditions Gives the embryo time to develop Provides time for dispersal

71 What brings about dormancy?
Growth inhibitors e.g. abscisic acid may be present in the seed and it prevents germination until it is broken down by cold, water or decay The testa (seed coat) might be impermeable to water or oxygen and it might take time for the testa to break down The testa might be too tough for the embryo to emerge. It will take time for the testa to soften.

72 Application in agriculture and horticulture
Some seeds need a period of cold before they germinate It may be necessary to break dormancy in some seeds before they are planted for agricultural or horticultural purposes This can be done by placing them in the fridge before they are planted

73 Germination The re-growth of the embryo after a period of dormancy, if the environmental conditions are suitable

74 Germination – Factors necessary
Water Oxygen Suitable temperature Dormancy must be complete

75 Germination – Factors necessary
Water Activates the enzymes Medium for germination reactions e.g. digestion Transport medium for digested products

76 Germination – Factors necessary
Oxygen Needed for aerobic respiration Suitable temperature Allows maximum enzyme activity

77 Events in Germination Digestion Respiration
Of stored food in endosperm and cotyledon Respiration To produce ATP to drive cell division Events in germination cease when the plants leaves have developed and the plant has started to photosynthesise

78 Events in Germination (detail)
Water is absorbed Food reserves are digested Digested food is moved to the embryo New cells are produced using amino acids Glucose is turned into ATP to drive cell division Radicle breaks through the testa Plumule emerges above ground New leaves begin to photosynthesise

79 Events in Germination Plumule Radicle Cotyledon

80 Events in Germination Plumule Radicle

81 Changes in dry weight of seeds during germination
Dry mass of seed (g) Time (days) Mass drops initially due to respiration of stored food, but then begins to increase due to photosynthesis

82 Changes in dry weight of seeds during germination
Embryo Dry mass of seed (g) Endosperm Time (days) Food reserves in endosperm are transferred to the growing embryo

83 Germination of broad bean (hypogeal)

84 Germination of broad bean (hypogeal)

85 Germination of broad bean
Ground Seed – water is absorbed through the micropyle

86 Germination of broad bean
The testa splits Radicle emerges

87 Germination of broad bean
Plumule emerges Radicle continues to grow

88 Germination of broad bean
The plumule is hooked to protect the leaves at the tip Epicotyl

89 Germination of broad bean
The plumule grows above the surface of the soil Lateral roots develop

90 Germination of broad bean
Plumule straightens and the leaves open out Throughout Hypogeal germination the cotyledons remain below the ground

91 Germination of sunflower (Epigael)
Seed – water is absorbed through the micropyle

92 Germination of sunflower
Radicle emerges

93 Germination of sunflower
Hypocotyl Hook

94 Germination of sunflower
Seed coat discarded Germination of sunflower Cotyledons Radicle grows downwards

95 Germination of sunflower
Leaves emerge Cotyledons wither In Epigeal germination the cotyledons rise above the ground

96 Learning Check Outline the main stages of sexual reproduction in plants

97 Review the plant life cycle
2 pollen is transferred 3 After fertilization flower withers 1 seeds develop in ovary 4 seeds disperse and germinate into new plant 4

98 Asexual Reproduction in Plants
Vegetative Propagation

99 Definition Asexual reproduction
does not involve the manufacture or union of sex cells or gametes e.g. binary fission, fragmentation, spore formation and budding It involves only one parent and offspring are genetically identical (have the same genetic content) to the parent

100 Vegetative Propagation
A form of asexual reproduction in plants Does not involve gametes, flowers, seeds or fruits Offspring are produced by a single plant (genetically identical to parent) Can happen naturally or it can be done artificially

101 Vegetative Propagation
Natural e.g. runners, tubers, plantlets, bulbs

102 What happens? Part of the plant becomes separated from the parent plant and divides by mitosis to grow into a new plant As a result the offspring are genetically identical to the parent

103 Parts of the parent plant may be specially modified for this purpose:
Stem Root Leaf Bud

104 Runners Modified Stems horizontal, running over the soil surface
terminal bud of the runner sends up new shoots e.g. strawberry, creeping buttercup.


106 Creeping buttercup

107 Modified Stem (continued)
Stem Tubers swollen underground stem tips buds (eyes) produce new shoots e.g. potato


109 2. Modified Roots Root Tuber swollen fibrous roots
the tuber stores food, but the new plant develops from a side bud at the base of the old stem e.g. dahlia, lesser celandine

110 Note: Tap Roots e.g. carrot and turnip, are swollen roots for food storage in biennial plants… they are not reproductive organs

111 3. Modified Leaves Plantlets
Some plants produce plantlets along the edges of the leaves Plantlets reach a certain size, fall off and grow into new plants e.g. Lily, kalanchoe (mother of thousands)

112 4. Modified Buds Bulbs A bulb contains an underground stem, reduced in size Leaves are swollen with stored food e.g. onion, daffodil, tulip

113 4. Modified Buds Bulbs The main bud (apical bud) will grow into a new shoot) The side buds (lateral buds) will also grow into new shoots



116 Comparison of reproduction by seed (sexual) and by vegetative propagation (asexual)

117 Advantage to seed formation
Sexual (seed) Asexual (vegetative) Cross pollination ensures variation (allows evolution) No variations – can be advantage in commercial horticulture More resistant to disease All plants are of same species susceptible to disease Dispersal reduces competition Overcrowding and competition Seeds can remain dormant and survive unfavourable conditions No seeds formed – no dormancy

118 Advantage to vegetative propagation
Sexual (seed) Asexual (vegetative) Complex process Simple process Depends on outside agents for seed dispersal No outside agents needed Slow growth of young plants to maturity Rapid growth Wasteful e.g. petals, pollen, fruit No waste

119 Vegetative propagation
Artificial used by gardeners to propagate plants e.g. cuttings, layering, grafting and budding

120 Cuttings Parts of a plant (usually shoots) removed from plant allowed to form new roots and leaves rooted in water, well-watered compost, or rooting powder e.g. busy lizzie, geranium


122 Grafting Part of one plant (scion) is removed and attached to a healthy, rooted part of a second plant (stock) Useful qualities from both plants combined into one e.g. rose flower and thorn-less stem e.g. apple trees


124 Layering A branch of a plant is bent over and pinned to the earth at a node When roots develop the branch is separated from the parent plant. Useful for the propagation of woody plants e.g. blackberry, gooseberry.


126 Micropropagation (Tissue Culture) (1/3)
Cells removed from plant and grown as a tissue culture in a special medium Growth regulators and nutrients added so that growing cells form a group of similar cells called a callus

127 Micropropagation (Tissue Culture) (2/3)
Different growth regulators are then added so that this tissue develops into a plantlet Plantlet can be divided up again to produce many identical plants Entire plant can be grown from a small piece of stem, leaf or root tissue Used in mass production of house plants and crops such as bananas and strawberries

128 Micropropagation (Tissue Culture) (3/3)
Provides a larger number of plants more quickly than cuttings. Can be used to check cells for a particular feature e.g. resistance to chemicals or a particular disease


130 Cloning All offspring genetically identical - produced asexually
Clones are produced by mitosis All the offspring from the various methods of vegetative reproduction (both natural and artificial) mentioned are examples of clones

131 END

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